The invention relates to an arrangement for interference suppression of electronic devices generating high-frequency noise voltages without mains disconnection at the input side, such as converter circuits. A shielded input and output electrically separated by means of transformers is employed together with filter circuits arranged at the input and output side.
Electronic circuits with semiconductors functioning as switches often represent high frequency sources of interference with an extensive frequency spectrum. In order to avoid radio interferences, the high frequency voltages on the input and output lines of such devices must be suppressed by means of special techniques.
The radio or electromagnetic shielding of mains-fed electronic devices of the type initially cited can present great difficulties when, upon observance of special regulations for the protective insulation of the devices, their reference potential dare not be connected to a grounded conductor. The techniques for sufficient electromagnetic shielding are made even more difficult in that electronic circuits are operated by the mains without electrical separation. The employment of filter circuits with large capacitances in the circuit of the mains lines cannot guarantee a sufficient suppression of the radio interference voltage, since high frequency noise voltages are unavoidably asymmetrically relayed by mains lines via winding capacitances of the transformer and other circuit capacitances.
In addition to these techniques, it is known from German AS 2,446,624, incorporated herein by reference, to completely shield the portion of the circuit which lies at the mains input side and at the output side. Such a shielding, however, has the disadvantage that, given high frequencies, the shield exhibit inductive reactances which are too high and, thus prevent a discharge of the high-frequency currents.